Abstract. The goal of this R61/R33 proposal is to carry out a phase IA/IB clinical study of AAVrh.10hFXN (a serotype rh.10 adeno-associated virus coding for human frataxin) to treat cardiac manifestations of Friedreich?s ataxia (FA), the most common inherited ataxia. FA is a fatal, presently, untreatable disorder. Most cases result from intron variants in the frataxin (FXN) gene; when inherited from both parents, there is resulting haploinsufficiency of FXN gene expression. While progressive neurologic disease limits mobility, cardiomyopathy is responsible for substantial morbidity and 60% of deaths secondary to progressive heart failure and arrhythmias. Cardiac MRI (CMR) data from our group and others demonstrate that FA-associated cardiomyopathy initially manifests with increased left ventricular (LV) myocardial mass (a potentially reversible phenotype) prior to development of myocardial fibrosis (irreversible damage). AAVrh.10hFXN, the therapeutic gene transfer vector to be used in the proposed human study, is a nonhuman primate-derived serotype rh.10 capsid with a constitutive promoter driving the normal human frataxin cDNA. AAVrh.10hFXN will be administered intravenously, a vector and route which in experimental animal models effectively delivers genes to the heart. Based on our preclinical efficacy data in two murine models in which intravenous AAVrh.10hFXN reverses the consequences of FA cardiomyopathy, together with extensive safety data, we are ready to initiate a phase IA/IB clinical trial with the following aims. R61 aim 1. Prepare and submit an Investigational New Drug package and gain approval from the FDA and other regulatory groups (Institutional Review Board, Biosafety) to initiate a phase IA/IB clinical trial. Milestone. Full regulatory approval to initiate parts A and B of the clinical trial, enroll the 1st subject in part A. R61 aim 2 and milestone. Manufacture clinical grade AAVrh.10hFXN for the part A (safety/dose-ranging) clinical trial. R33 aim 3. Carry out the part A (safety/dose-ranging) trial to determine the maximum tolerable dose of AAVrh.10hFXN therapy for the cardiac manifestations of FA. Milestone. Initiate and complete assessment of n=9 individuals (3 doses, 3 each), with an audited final report. R33 aim 4 and milestone. Manufacture clinical grade AAVrh.10hFXN for part B (safety/preliminary efficacy) clinical trial. R33 aim 5. Carry out the part B safety/preliminary efficacy study at the highest tolerable dose from part A. Milestone. Complete assessment of n=15 individuals, with an audited final report. Given that genetic variance is responsible for many forms of cardiomyopathy and that existing treatments are limited, this study offers a potential therapeutic paradigm shift to reverse cardiac phenotype and thus improve clinical outcomes for a broad range of patients with genetically mediated cardiomyopathies at risk adverse LV remodeling and its devastating clinical consequences.